The present invention relates to a novel absorption refrigerator and, more particularly, to an absorption refrigerator which has excellent corrosion resistance properties, with main structural components of the absorption refrigerator being highly protected from corrosion by forming in advance corrosion protective films on surfaces of the main structural components, and the invention relates to a method of manufacture of the absorption refrigerator.
Absorption refrigerators each use a rich LiBr solution as an absorption solution and water as a refrigerant. In the absorption refrigerator, in general, the higher the concentration of the LiBr solution is, the higher the efficiency of refrigeration becomes, so that the concentration and temperature of the LiBr reach to 65% and 160xc2x0 C., respectively, at the highest temperature portion of a double effect absorption refrigerator, for example. Under such circumstances, the structural members of the refrigerator tend to become seriously corroded. Therefore, a suitable inhibitor, such as tungstate, molybdate has been added to the solution, as disclosed in JP A 58-224186 and JP A 58-224187, whereby corrosion has been reduced. The inhibitor is used together with the hydroxide of an alkaline metal, which is a pH adjuster and forms corrosion protective films on the members due to the oxidizing force thereof, whereby corrosion is suppressed.
Apart from a method of forming a corrosion protective film during operation of a refrigerator, there is a method in which, as disclosed in JP A 1-121663, JP A 2-183778, in order to form a corrosion protective film on an inner wall of a high temperature regenerator, in contact with a most highly corrosive absorption solution therein before operation of the refrigerator, a film forming liquid recirculation line and a refrigerant supply line are provided in the high temperature regenerator, and a film coating operation is carried out by recirculating a film forming liquid, heated and concentrated in the high temperature regenerator, through the film forming liquid recirculation line, whereby corrosion protective films are coated on the inner wall of the high temperature regenerator and the surfaces of the piping of the recirculation lines which are in contact with the absorption solution.
Further, as a corrosion protective film coating method which does not use an absorption solution, there is a method in which a corrosion protective film is formed in the interior of a refrigerator by heating it to 400xc2x0 C. or more under a gas atmosphere in which the dew point thereof is controlled so that the partial pressure of steam becomes 10 ppm or less and the partial pressure of oxygen is adjusted to about 10 Pa-10 kPa, as disclosed in JP A 6-249535.
As for a method of forming a corrosion protective film using an inhibitor during operation of a refrigerator, in a case wherein chromate and nitrate are used as the inhibitor, it is feared that pitting may occur in the structural material when the concentration of the inhibitor reaches a certain level or more, and so there remains a problem of management of the inhibitor concentration when an inhibitor is used. On the other hand, since molybdate has a low solubility to LiBr and the oxidation is weak, there remains a problem in that much time is required to form a stable corrosion protective film, and the refrigeration efficiency decreases due to generation of hydrogen gas during formation of a stable corrosion protective film, whereby it is difficult to attain a sufficient corrosion protective effect. Further, a relatively large amount of inhibitor is consumed by the time a stable corrosion protective film is completed, so that it is necessary to add inhibitor.
As disclosed in the above-mentioned prior methods, there is a method of forming a corrosion protective film by performing a film forming operation using a film forming liquid recirculation line before operation of the whole refrigerator, in order to solve the above-mentioned problems. In this method, however, since the film forming liquid used in the film forming operation is a LiBr solution including molybdenum, as used in the method of forming a corrosion protective film during operation of the refrigerator, the problem of a decrease in refrigeration efficiency due to generation of hydrogen gas during the operation can be solved, however, other problems are still left unsolved in that much time is required for forming a corrosion protective film due to the low solubility of molybdate, the fact that the oxidation also is weak, and in that much inhibitor is consumed.
The corrosion protective film formation method which does not use an absorption solution and is disclosed in the above-mentioned prior art can solve the problem that much time is required to form a corrosion protective film because of the low solubility of molybdate and the weak oxidation, and the problem that a relatively large amount of inhibitor is consumed. However, the step of injecting an inert gas in order to control the dew point, the step of condensing steam to lower the pressure to a prescribed level or lower, the step of injecting oxygen gas to a prescribed pressure, etc. are needed, so that the corrosion protective film forming method becomes not only complicated, but various apparatuses are required, such as a vacuum pump, a pressure gauge, a mass analyzer, a cold trap, etc., and so the refrigerator becomes complicated in construction and high in cost. Further, in a method in which an interior of a refrigerator first is filled with an inert gas (since the inert gas is introduced after reduction of the pressure, the inert gas is replaced with gas in the entire interior of the refrigerator) and then oxygen gas is injected, even if oxygen is caused to flow therein, the oxygen gas does not enter all gaps and convection portions in the interior of the refrigerator, so that it is difficult to make the partial pressure of oxygen uniform in the refrigerator. Therefore, in some portions, a corrosion protective film is formed by excessive oxygen, but some other portions lack oxygen, so that a sufficient corrosion protective film is not formed or an incomplete corrosion protective film is formed, and so corrosion is not suppressed.
An object of the present invention is to provide an absorption refrigerator in which reduction of the refrigeration efficiency due to generation of hydrogen gas during the operation thereof is prevented, and in which a high corrosion resistance due to the provision of corrosion protective films is attained, such as by use of thin and uniform corrosion protective films of high corrosion resistance, formed on surfaces of the absorption refrigerator in an easy manner before operation thereof, and it is an object to provide a method of manufacturing such an absorption refrigerator.
The above-mentioned object can be achieved by forming a corrosion protective film on an absorption refrigerator by bringing high temperature steam or air having an arbitrary dew point into contact with structural material of the absorption refrigerator before operation of the refrigerator.
More specifically, the object is achieved by provision of an absorption refrigerator having a corrosion protective film formed by bringing steam of 200-800xc2x0 C. (preferably 330-500xc2x0 C., more preferably 350-450xc2x0 C.) or air having an arbitrary dew point, into contact with structural material of the absorption refrigerator before operation of the refrigerator, a method of forming a corrosion protective film by causing the above-mentioned steam or air having an arbitrary dew point to contact the structural material of the absorption refrigerator, and an apparatus for introducing the above-mentioned steam or air of an arbitrary dew point for practicing the method. The method of bringing the above-mentioned steam or air having an arbitrary dew point into contact with structural material of the absorption refrigerator can be achieved by a method of preventing corrosion by providing a gas introduction inlet in the absorption refrigerator and introducing the above-mentioned steam or air of an arbitrary dew point through the gas introduction inlet, and by forming a corrosion protective film on a surface of each part of a high temperature regenerator, high temperature heat exchanger, low temperature heat exchanger, etc. by exposing the surface of each part to an atmosphere containing the above-mentioned steam or air of an arbitrary dew point, and then assembling the parts having the surfaces which have corrosion protective films formed thereon.
The present invention resides in an absorption refrigerator which uses water as a refrigerant and a halogen compound as an absorption solution, and which is characterized in that an oxide film having a thickness of 0.02-5.0 xcexcm, preferably 0.1-2.5 xcexcm, more preferably 0.3-2.0 xcexcm, and any color of blue, purple, black and gray, or a hydroxyl group, is formed on a surface of at least one of a heat exchanger and a high temperature regenerator, or all the surfaces, contacting the above-mentioned absorption solution, of the iron or iron containing structural material constituting the refrigerator.
Further, the present invention is characterized in that an oxide film formed on a surface, in contact with an absorption solution, made of iron or iron-containing components constituting the absorption refrigerator, is thinner than an oxide film formed on a surface of an iron or iron-containing component constituting piping forming a cooling water line with a cooling tower, a cold water line and a steam line.
Further, the present invention resides in an absorption refrigerator comprising a high temperature regenerator for heating a water solution having a halogen compound to generate steam, a condenser for condensing the steam, a low temperature regenerator for cooling the steam, an evaporator for evaporating the water from the condenser and producing cold water, an absorber for absorbing the water from the evaporator into a water solution including a high concentration halogen compound, and a heat exchanger for returning the refrigerant issued from the absorber to the high temperature regenerator and effecting heat exchange between the water from the low temperature regenerator and the refrigerant from the absorber, characterized in that an oxide film having thickness of 0.02-5.0 xcexcm, and any color of blue, purple, black and gray, or a hydroxyl group, is formed on a surface of at least one of the high temperature regenerator and heat exchanger, or on at least a portion in contact with the water solution, steam or water and made of iron or an iron-containing material, of the high temperature regenerator, condenser, low temperature regenerator, evaporator, absorber and heat exchanger.
In accordance with the present invention, it is possible to form the above-mentioned corrosion protective film, such as an oxide film on each of the parts constituting each apparatus, other than the high temperature regenerator and heat exchanger, and then to assemble them into a whole apparatus.
The present invention resides in a method of production of an absorption refrigerator, which uses water as a refrigerant and a halogen compound as an absorption solution, characterized by oxidizing a surface of at least one of the heat exchanger and the high temperature regenerator at a temperature of 200-800xc2x0 C., and adjusting the heating temperature and the heating retaining time so that the value of a parameter (P), obtained according to P=T (5+log t), is 3.5-6.0xc3x97103, preferably 4.0-5.5xc3x97103, and more preferably 4.4-5.0xc3x97103, wherein T represents the heating temperature (xc2x0K), and t represents the heating retaining time (minute), or by heating the surface of at least one of the heat exchanger and the high temperature refrigerator in an oxidizing atmosphere in which the partial pressure of steam is 0.000 or more and the partial pressure of oxygen is 0.2 or more, thereby to form an oxide film thereon.
The present invention resides in formation of an oxide film on one of the heat exchanger and the high temperature regenerator, or on at least a portion thereof in contact with the water solution, steam or water and which is made of iron or iron-containing material, of the high temperature regenerator, condenser, low temperature regenerator, evaporator, absorber and heat exchanger, or in producing individually each of the structural components.
In the absorption refrigerator according to the present invention, lithium bromide is used as the halogen compound for forming an absorption solution of the absorption refrigerator, and so corrosion is produced by the lithium bromide due to adhesion of bromine ions of high concentration on the structural material. In general, the corrosion rate is faster at an initial stage and it decreases with passage of time. This is because an oxide film is formed on a surface of the material with the passage of time, and the oxide film works as a corrosion protective film. That is, when a corrosion protective film is formed, the diffusion of water, oxygen, oxygen ions, iron ions, etc., which influence corrosion, is suppressed by the corrosion protective film. Therefore, by forming in advance a corrosion protective film on a surface of the structural material by pre-oxidation, direct adsorption and contact of bromine ions onto the surface of the structural material can be prevented, whereby corrosion can be prevented. Iron or iron-containing material is used for many of the structural materials. Iron oxide obtained by directly oxidizing the structural material can be used for a corrosion protective film. The corrosion resistance of the corrosion protective film is influenced by not only the chemical property of the film but by the physical property of the film as well. That is, as mentioned above, since the corrosion protective film suppresses diffusion of substances influencing corrosion, as mentioned above, a corrosion protective film which is denser has a higher diffusion suppressing ability. Even if the oxide film is made thicker, the corrosion resisting effect by the oxide film is small without sufficient denseness in the oxide film. Further, in the case where a hydroxyl group exists on the surface, a strong hydrogen binding occurs in the film by protons of the hydroxyl group and a film of high corrosion resistance is formed.
As methods of forming such a corrosion protective film, there are a method of using high temperature water and a method of using high temperature gas. In the case of high temperature water, a problem occurs in that a high temperature and high pressure vessel is needed, thus a large sized equipment is necessary. On the contrary, in the case where air (partial pressure of steam is controlled, air of an arbitrary dew point) or steam is used as the high temperature gas, since the oxygen potential and partial pressure of the steam can be controlled arbitrarily, the equipment becomes simple and the method can be easily put into practice. Further, since a refrigerator or its components in an air atmosphere are oxidized as they are, there is an oxygen potential to the partial pressure of oxygen in the air, at least, so that oxide film formation does not become incomplete because of lack of oxygen. Further, it is important to make the oxide film which is formed in such atmosphere very thin, for example, about several ten thousands angstrom, whereby an oxide film of high density can be obtained, allowing it to work as a corrosion protective film of high corrosion resistance.
In the case where stainless steel or a low alloy steel is used for the structural material, also, the above-mentioned high temperature gas can be used as the pre-oxidizing means in the same manner as described above.
Further, in case where the oxidation is performed before operation of the refrigerator, that is, in case of pre-oxidation treatment being performed, since a film is formed in the pre-oxidation treatment, the inhibitor is almost not consumed at all even in an initial stage, so that it is unnecessary to supplement the inhibitor. By forming the corrosion protective film before operation of the refrigerator, it is unnecessary to worry about corrosion of the structural material from an initial stage of operation of the refrigerator, and it is possible to enhance the reliability of the product.
In the method of forming a relatively thick corrosion protective film, using gas as disclosed in the above-mentioned prior art, once an inert gas is filled, and then oxygen gas is filled, because separation occurs in the corrosion protective film being formed on the surface to be protected from corrosion, the film becomes nonuniform. On the other hand, in accordance with the present invention, as mentioned above, a relatively thin film is formed. In this method, high temperature steam, air of an arbitrary dew point or oxygen gas is introduced into a portion in which air was previously filled, so that the oxygen partial pressure in the atmosphere exists to a greater extent than the oxygen partial pressure in the air, at least, and it does not occur that the corrosion protective film is not formed due to lack of the oxygen partial pressure. Therefore, a uniform corrosion protective film can be formed.
As an absorption solution, a solution comprising, by weight, lithium bromide 50-70%, alkaline metal hydroxide 0.05-1%, molybdate 10-150 ppm as MoO42xe2x88x92, nitrate 5-350 ppm as NO3xe2x88x92, higher alcohol 0.2-3%, and balance water 30% or more is preferable.
An absorption refrigerator may be classified according to power source, use and construction, as expressed in TABLE 1. Except for a small amount of electric power for driving auxiliary apparatuses, it is almost not necessary to use electric power. As a power source, many kinds of substances, such as gas, oil or steam, can be used.
Basically, it is an object for the absorption refrigerator to produce cold water for cooling, but the apparatus can be used for various objects, such as production of hot water for heating in winter, or synchronized utility of cold water and hot water by one apparatus.
Since the absorption refrigerator uses water as a refrigerant and a lithium bromide solution as an absorption solution, the pressure within the refrigerator during operation thereof is at atmospheric pressure or less, and so the refrigerator can not be a pressure vessel. Therefore, as for an operation qualification, there is no need for an operation qualification particular to the absorption refrigerator.
As for rotating parts, only small capacity pumps are needed for recirculation of refrigerant and solutions, so that the refrigerator has advantages, such as less noise and less vibrations, as compared with any mechanical refrigerator.
A typical absorption refrigerator, apparatuses and devices of a direct double effect absorption cold-hot water unit will be explained hereunder.
The unit comprises a main body in which four heat exchangers of an evaporator, an absorber, a condenser and a low temperature regenerator are incorporated into one shell, a high temperature regenerator, a refrigerant pump and a solution pump for recirculating a refrigerant and solutions in the apparatus, respectively, and a solution heat exchanger for effecting heat exchange between solutions.
In the evaporator, water as a refrigerant is sprayed over a bundle of tubes under a vacuum of about 1/100 atmospheric pressure, and, at this time, evaporation heat is received from the cold water flowing in the bundle of tubes to evaporate the refrigerant, so that the cold water in the bundle of tubes is cooled, whereby the apparatus is to be used for an object of cooling air.
In the absorber, since a lithium bromide solution cooled to a proper temperature by the cold water flowing in the tubes is at a saturated pressure a little lower than in the evaporator, refrigerant vapor generated in the evaporator flows into the absorber to be absorbed in the solution. The dilute solution which absorbs the refrigerant to be diluted is divided into two flows which are transferred into the high temperature regenerator and the low temperature regenerator, respectively. The divided and diluted solutions are heated and concentrated in the high and low temperature regenerators, respectively, to become concentrated solutions, and then are returned to the absorber again.
In the high temperature regenerator, a heat source, such as gas or oil, is supplied from outside and burned in a furnace. The dilute solution is concentrated by this heat, and vapor generated incidentally at this time is passed through tubes of the low temperature regenerator and utilized as a heating and concentrating source for the low temperature generator.
Vapor generated outside the tubes of the low temperature regenerator is liquified in the condenser and returned into the evaporator, whereby one cycle is completed.
Classifying roughly the method of transferring the diluted solution from the absorber into the two regenerators, there are two ways, one of which is a parallel flow type in which the solution is divided into two and transferred in parallel, and the other is a series flow type in which the solution is sent into the two regenerators in series. In the former, the operation pressure in the high temperature regenerator during operation is lower as compared with that in the latter and larger in margin to the atmospheric pressure, so that it is easy to operate the apparatus, and the amount of the solution recirculating in the cycle is small, so that it has an advantage that a heat exchange of small size is sufficient for attaining the same efficiency.
Direct boiling double effect absorption type cold hot water unit:
The unit is a main heat source apparatus which is widely used for cooling and heating in general buildings. The unit is used for energy conversion, serving in place of an electric power source at the peak of electric power demand in summer. Since energy saving also is desired, there is a special energy saving type unit in which the efficiency is raised by recovering energy of combustion exhaust gas in the high temperature regenerator.
Further, the unit of this type has the widest application fields, and it can be employed for a unit commonly used for both solar heat and direct boiling type in which solar heat is applicable, a switching combustion type in which fuel can be switched between gas and oil, an outdoor type, a cold hot water simultaneous supply type, etc.
Steam double effect, steam single effect absorption refrigerator:
In the double effect steam boiling apparatus, steam at a pressure of 8 kg/cm2 G is used. However, there is a low pressure steam double effect absorption refrigerator which is operable at a pressure of 5 kg/cm2 G, using the advantage of parallel flows, as mentioned above, or at pressure of 2 kg/cm2 G, selecting a suitable temperature of cooling water for cold water.
Further, in a factory having an extra amount of steam of 1 kg/cm2 G, a single effect absorption refrigerator is effective.
Exhaust gas-used absorption refrigerator, cold hot water unit:
This is a refrigerator which uses as a heat source exhaust gas from a diesel engine or gas turbine, or exhaust gas from various kinds of factories. The exhaust gas also can be used for a double effect refrigerator if the temperature is 250xc2x0 C. or higher.
As for construction of the apparatus and devices thereof, a high temperature regenerator portion of the double effect absorption refrigerator type hot water unit can be replaced by an exhaust gas heat recovery apparatus. The exhaust gas heat utilizing portion can be replaced by other heat source, such as steam, gas, oil, etc.
Solar absorption refrigerator:
Since the temperature of hot water heated by solar heat is about 85xc2x0 C., which is relatively low, it is used for a single effect type refrigerator. However, since the heat source is unstable, it is necessary to provide some type of back up system. A solar heat jointly used direct boiling absorption refrigerator is most suitable therefor. When solar heat is insufficient, the direct boiling double effect refrigerator can back up it, so that it is most advantage in equipment cost and operation cost.
Absorption heat pump:
The absorption refrigerator is a machine for pumping heat from a low temperature heat source to a high temperature portion using some power source, and the refrigerator uses heat absorption in the low temperature portion, although, heat release in the high temperature portion can be used. As for heat balance in the refrigerator, since the sum of the heat amount of power required for pumping heat and the heat amount pumped from the low temperature portion is equal to the amount of the heat release at the high temperature portion, it can be improved by 1.5-2 times as compared with the case in which the power source is simply used for heating. This is an absorption type heat pump, which can be used mainly for a factory process, a heating arrangement using pre-heated boiler feed water.